Is there such a thing as policy routing across a dynamic routed network, in this case OSPF? The more research I do, the more I'm thinking 'no.' Or, at least, 'No, you can policy route at your network's gateway.'

Say you have a mesh of routers, each router talks to one or more other routers. So, any given router is going to have multiple paths to router X, which is the gateway to another network. Great. So any router can probably talk to router X, and if a given link goes down, OSPF will find a way around it.

Now, lets say you have router Y, which is a gateway to a different network. Based on the IP address (each router is set up to listen to multiple subnets) you may want the packets to go out router X, you may want them to go out router Y.

As near as I can tell, the only way to do this would be to plug router Y into router X, and do policy routing on router X.